Parahisian Pacing

From Ask Dr Wiki

Parahisian Pacing for AS pathway

High output captures His resulting in narrow QRS and lower output captures Ventricle.

If no change in Stimulus to A interval when changing from high output to low output then Anteroseptal pathway is present.

An increase in the VA interval without change in the retrograde activation sequence means absence of a Septal AP

Example of Parahisian Pacing with No Evidence of an Accessory Pathway

Notice in the 1st and 2nd beats the His is captured resulting in a narrow QRS complex. In the 3rd and 4th beat we lose His capture and only capture the local ventricle resulting in a wider QRS with a retrograde His seen in His distal on the image above. The Stim to A with His capture is 103 ms and the Stim to A without His capture is 133 ms meaning that there is absence of a septal pathway.